1. Field of the Invention
The present invention relates to drive positioning using a stepping motor and in particular to a stepping motor control system having reduced positioning and stopping time.
2. Description of the Prior Art
In head positioning and drive of a small-sized disk unit, for example, stepping motors have been widely used.
An example of the conventional stepping motor control system for head positioning and driving used in such a disk unit will now be described. In FIG. 1, a controller 1 supplies a rotation direction signal a and a drive step number signal b to the microcomputer 2. In response thereto, the microcomputer 2 defines the optimum pulse rate pattern and supplies phase excitation changeover signals c and d to a driver 3.
When the signal c is "H", the driver 3 lets flow a current through a .phi..sub.1 -phase coil of a stepping motor 4 in a direction represented as .phi..sub.1 .fwdarw..phi..sub.1. When the signal c is "L", the driver 3 lets flow a current in the opposite direction represented as .phi..sub.1 .fwdarw..phi..sub.1. When the signal d is "H", the driver 3 lets flow a current through a .phi..sub.2 -phase coil of the stepping motor 4 in a direction represented as .phi..sub.2 .fwdarw..phi..sub.2. When the signal d is "L", the driver 3 lets flow a current in a direction represented as .phi..sub.2 .fwdarw..phi..sub.2.
As a result, the pulse motor 4 is rotated in a predetermined direction by as many steps as supplied from the controller 1. Thus the head of the disk unit is driven to be positioned at a predetermined position. The head drive and positioning operation at this case is referred to as "seek".
FIG. 2 shows the above described pulse rate pattern. In the starting acceleration region, the pulse rate is so raised that the acceleration may be constant from a low velocity up to a predetermined velocity to prevent the stepping motor 4 from getting out of step.
Subsequently, the pulse motor 4 stays in the fixed velocity region until the total number of seek steps minus the number of steps required for deceleration is reached. In the fixed velocity region, the pulse rate is held at a predetermined constant value to seek the head at the uniform velocity.
In the deceleration region, the pulse rate is lowered at a predetermined rate to seek the head with the uniform deceleration. And the head is stopped at the target position to be positioned.
Increase or decrease in the number of seek steps, i.e., increase or decrease in the distance the head moves is dealt with by changing the number of steps included in the fixed velocity region so as not to change the curves of acceleration and deceleration. When the number of seek steps has become smaller than the sum of the number of steps included in the acceleration region and the number of steps included in the deceleration region, however, the acceleration region is immediately succeeded by the deceleration region as represented by broken lines 1 to 4 in FIG. 3. That is to say, control is effected by the so-called triangular seek.
Therefore, the control procedure of the microcomputer 2 at this time is represented by FIG. 4.
In the deceleration region, the rotation angle of the stepping motor 4 changes as shown in FIG. 6. As well known, the stepping motor is configured to successively rotate while taking discrete stationary stabilized angles each time the phase excitation is changed over, i.e., for each step. In the prior art, therefore, the step commands are so supplied as to form stairs as represented by A of FIG. 5. The rotation of the stepping motor follows it as represented by B of FIG. 5.
In this control system of the prior art, therefore, the rotation angle of the stepping motor becomes oscillatory as represented by a period C of the rotation angle characteristics B after the stepping motor 4 reaches the target rotation angle position and the stepping operation is stopped, i.e., the phase excitation state is stationary. It thus takes long time for the motor to converge to the target angle position and stop, the so-called settling time being elongated.
In disk units or the like, the settling time at the completion of the head seek is desired to be short as far as possible.
In a widely used method heretofore, therefore, a mechanical damper is added to the drive section.
However, the use of the mechanical damper results in large-sized units. Therefore, it is desirable to remove the mechanical damper to attain the smallsized system.
If the mechanical damper is removed, however, the settling becomes very long, resulting in long access time.
Therefore, a small-sized disk unit using a stepping motor of the prior art has a problem that it is difficult to shorten the access time.
Such a disk unit is disclosed in Japanese Patent Unexamined Publication No. 122270/80, for example.